A surface acoustic wave that is a kind of ultrasonic vibrations is utilized for devices such as filters, resonators or the like for communication purpose. Also, extensive studies have been made on applications to sensors, actuators, etc.
As illustrated in FIG. 18, a surface acoustic wave can be generated on a surface of a piezoelectric substrate 2 by applying alternating voltage between interdigital transducers 11 having alternating finger electrodes formed on the piezoelectric substrate 2.
At this time, strains 12 in opposite directions to each other are caused on the piezoelectric substrate 2 at locations near the minus and plus finger electrodes due to electric field 13 at the peripheral areas of such finger electrodes as shown in FIG. 19. The plus/minus polarities of the finger electrodes 11 reverse depending on the alternating voltage and thus orientations of the strains 12 that occur near the finger electrodes 11 periodically reverse, thereby causing a surface acoustic wave on the piezoelectric substrate 2. The frequency of the surface acoustic wave is determined by the geometry (i.e., pitch of the finger electrodes) of the interdigital transducer 11 and the generated surface acoustic wave propagates in the left-right directions in FIG. 18. In other words, the piezoelectric substrate 2 also acts as a medium for propagating the surface acoustic wave. When the surface acoustic wave propagates on the piezoelectric substrate 2, an elliptical movement of particles occurs near the surface of the piezoelectric substrate 2 as graphically illustrated in cross section view in FIG. 20.
In case of communication filters, receiving interdigital transducers having the identical geometry are disposed on the piezoelectric substrate 2 at a distance from the interdigital transducers 11 for converting the surface acoustic wave propagated on the piezoelectric substrate 2 into an electrical signal in the receiving interdigital transducers.
The non-patent document 1 as listed hereinafter discloses “a surface acoustic wave linear motor” utilizing wave-phenomenon of a surface acoustic wave. The motor comprises a slider as a diving member disposed on a piezoelectric substrate on which the surface acoustic wave propagates. Upon pressing the slider onto the piezoelectric substrate, elliptical movement of particles on the surface of the piezoelectric substrate is transmitted to the slider by way of friction, thereby moving the slider in the opposite direction to the direction of propagation of the surface acoustic wave.
The reference document 2 as listed hereunder discloses “a tactile display” utilizing wave phenomenon of a surface acoustic wave. This device is designed to generate a vibration on the surface of a finger skin by utilizing a mechanical vibration of a surface acoustic wave that propagates on a piezoelectric substrate. The device can be attached to a button on a mouse of a PC (personal computer). When the operator traces a non-flat surface displayed on the PC display screen with a cursor using the mouse, a SAW driving signal of the device is modulated in accordance with the cursor position, thereby enabling the operator to feel at his/her finger-tip the roughness of the displayed surface.
A piezoelectric single-crystal substrate such as LiNb03 or the like is widely used as the piezoelectric substrate for efficiently exciting a surface acoustic wave. Discovered more recently are materials having high electromechanical coupling coefficient in the cutting orientation of the crystal such as KNb03 or the like, that are expected to be more useful.
In a device utilizing a surface acoustic wave on a non-piezoelectric material, known is a touch panel that utilizes a surface acoustic wave for detecting touched positions as disclosed in the non-patent document 3 that is listed hereunder. As illustrated in FIG. 21, this device comprises a glass substrate 30 that enables to propagate a SAW, a pair of driving electrodes 31 and a pair of receiving electrodes 32 disposed at the periphery thereof in an opposed relationship to each other. The driving electrodes 31 and the receiving electrodes 32 comprise interdigital transducers 111 that are bent at generally right angles. The interdigital transducers 111 are formed on a piezoelectric thin film 21 that is formed on the electrode area on the glass substrate 30. A surface acoustic wave generated from the driving electrodes 31 propagates on the surface of the glass substrate 30 before being received by the receiving electrodes 32. However, when touched by a finger, the surface acoustic wave propagating on the glass substrate 30 at the touched position is attenuated. Such receiving signal is analyzed for detecting the touched position.
A touch panel utilizing a surface acoustic wave is also disclosed in the patent document 1 as listed hereunder. The touch panel comprises a plurality of piezoelectric plates having interdigital transducers formed thereon and the piezoelectric plates are firmly attached to the peripheral areas of a glass substrate with the interdigital transducers facing the glass plate.
Also disclosed in the patent document 2 as listed hereunder is an ultrasonic transducer comprising a piezoelectric thin plate having the thickness of about 220 micrometer (μm) and interdigital transducers formed thereon and a glass substrate, wherein the piezoelectric thin plate and the glass substrate are adhered to each other using epoxy resin in such a manner to sandwich the interdigital transducers therebetween.
The patent document 3 as listed hereunder also discloses a piezoelectric device comprising about 200 micrometer (μm) thick piezoelectric plate having interdigital transducers formed thereon and a glass substrate having grooves on the surface to contact with the piezoelectric member, wherein the surface of piezoelectric member opposite to the electrodes and the glass substrate are jointed to each other by way of a molten metal layer.    Patent document 1: JP 2002-196876 A    Patent document 2: JP H06-46496 A    Patent document 3: JP 2003-8094 A    Non-patent document 1: http://www.intellect.pe.u-tokyo.ac.jp/research/sawmotor/sawmotor-j.html “Surface acoustic wave linear motor”    Non-patent document 2: http://www.intellect.pe.u-tokyo.ac.jp/reserch/saw-tactile/saw-tactile-j.html “Tactile display using surface acoustic wave”    Non-patent document 3: http://pcweb.mycom.co.jp/news/2002/11/26/14. html “Clear touch panel for PDA of 98% light transmissivity”
However, piezoelectric single-crystalline substrates are difficult to fabricate and available maximum wafer size is limited to about 10 cm (or 4 inches) in diameter, thereby making the cost per substrate expensive.
In case of applying mechanical vibration of a surface acoustic wave to electro-mechanics (or mechatronics), it is required to excite surface acoustic wave over a wide range and propagate surface acoustic wave over a long distance. However, such applications are restricted by the size of piezoelectric single-crystalline substrates that excite a surface acoustic wave.
Although a surface acoustic wave is excited on a glass substrate in the touch panel as disclosed in the aforementioned non-patent document 3, the power of the surface acoustic wave propagating on the glass substrate is weak and thus making it impossible to extract the mechanical energy of a surface acoustic wave from such device for electro-mechanics applications.
Similarly, it is impossible to generate a surface acoustic wave having a strong power on the glass substrate in the prior art as disclosed in the aforementioned patent documents 1-3.